Respiratory therapy systems are designed to assist a patient who has difficulty breathing or is unable to breath. In general terms, respiratory therapy systems include a ventilator, an optional humidifier including a heater plate, and a patient circuit. When a humidifier is used, the ventilator supplies gases to a humidification chamber coupled with the humidifier. Water within the humidification chamber is heated by the humidifier heater plate, which produces water vapor that humidifies gases passing through the chamber. From the chamber, humidified gases are then delivered to the patient through the breathing circuit. One or more breathing tubes of the patient circuit may be heated to maintain a desired temperature of gas (as used herein, the term “gas” can comprise a single type of gas (e.g., oxygen) or a mixture of multiple types of gases (e.g., a mixture of helium and oxygen) within the one or more breathing tubes.
Current respiratory therapy systems (either with or without a humidifier), utilize one or more sensors to measure various parameters associated with gas in the systems. Quantitative measurement of parameters acquired from one or more sensors are used to control the systems output to a desirable set point. Example parameters may include relative humidity, temperature, flow, pressure, etc. The one or more sensors are positioned within an airway of the patient circuit and are integrated with a sensing element to measure parameters. During the coarse of delivering the humidified gases, within the airway of the breathing tubes, the integrated sensing element of the sensor(s) can be subjected to contamination due to introduction of various particles (e.g., water, salt, aerosolized medicine). The accumulation of contamination on the sensing element over time can cause incorrect measurements, ultimately resulting in improper operation and/or failure of the respiratory therapy system. For example, a safety critical feedback sensor, once subjected to contamination, can produce a signal that is drastically higher or lower in relation to a controlled system output set point, resulting in potentially unsafe output of the system (e.g., incorrect medication dosage, elevated temperature, lower temperature, etc.).
In general, contamination accumulation may occur from residual water and particulates that forms a film on the sensor/sensing element surface for the inter and/or intra respiratory therapy session. For example, residual water on the sensor, after a therapy session, dries off, leaving a film of water marks, salt residue, etc. on a sensor surface. This film can impede the sensing capability of the sensor. For example, a capacitive membrane sensor absorbs and releases water relative to an environmental humidity. The change in capacitance produces electrical signals proportional to a calibrated voltage (or current) threshold. The accumulation of residual contamination can shift the signal threshold and could result in erroneous and/or erratic operation of a control system output.
When using an integrated relative humidity/temperature sensor, failure of the sensor can be especially prevalent when exposed to residual contamination accumulated over time, either intra-therapy (during use) or post therapy session (after use or many uses). In particular, residual contamination can cause output of a sensing element to shift (or fail) from calibrated values resulting in dangerously high outputs, which can compromise patient safety. For example, contamination on a surface of the sensor (e.g., a capacitive or resistive membrane) can result in incorrect delivery of elevated gas temperatures for an extended period of time to the patient. This situation can be undesirable and potentially cause damage to epidermal cells of the patient.